Generally, fine pattern formation is carried out by the photolithography in manufacturing processes of a semiconductor device. A number of substrates called photomasks are normally used for this fine pattern formation. The photomask comprises generally a transparent glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the photomask.
In the manufacture of a photomask by the photolithography, use is made of a photomask blank having a thin film (e.g. a light-shielding film or the like) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate. The manufacture of the photomask using the photomask blank comprises an exposure process of applying required pattern writing to a resist film formed on the photomask blank, a developing process of developing the resist film according to the required pattern writing to form a resist pattern, an etching process of etching the thin film according to the resist pattern, and a process of stripping and removing the remaining resist pattern. In the developing process, a developer is supplied after applying the required pattern writing (exposure) to the resist film formed on the photomask blank to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. In the etching process, using this resist pattern as a mask, an exposed portion of the thin film, where the resist pattern is not formed, is dissolved by dry etching or wet etching, thereby forming a required mask pattern on the transparent substrate. In this manner, the photomask is produced.
For miniaturization of a pattern of a semiconductor device, it is necessary to shorten the wavelength of an exposure light source for use in the photolithography in addition to the miniaturization of the mask pattern formed in the photomask. In recent years, the wavelength of an exposure light source in the manufacture of a semiconductor device has been shortened from a KrF excimer laser (wavelength 248 nm) to an ArF excimer laser (wavelength 193 nm).
As a type of photomask, a halftone phase shift mask is known apart from a conventional binary mask having a light-shielding film pattern made of a chromium-based material on a transparent substrate. This halftone phase shift mask is configured to have a light-semitransmitting film on a transparent substrate. This light-semitransmitting film is made of, for example, a material containing a molybdenum silicide compound or the like and is adapted to transmit light having an intensity that does not substantially contribute to exposure (e.g. 1% to 20% at an exposure wavelength) and to give a predetermined phase difference to this transmitted light. By means of light-semitransmitting portions formed by patterning the light-semitransmitting film and light-transmitting portions formed with no light-semitransmitting film and thus adapted to transmit exposure light, the halftone phase shift mask provides a relationship in which the phase of the light transmitted through the light-semitransmitting portions is substantially inverted with respect to the phase of the light transmitted through the light-transmitting portions (i.e. shifts the phase). As a consequence, the lights having passed near the boundaries between the light-semitransmitting portions and the light-transmitting portions and bent into the others' regions due to the diffraction phenomenon cancel each other out. This makes the light intensity at the boundaries approximately zero to thereby improve the contrast, i.e. the resolution, at the boundaries.
In recent years, there have also appeared a binary mask for an ArF excimer laser using a material containing a molybdenum silicide compound as a light-shielding film, and the like.